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Steien Network Arch Bridge ICTB 2013
Johannes Veie Norwegian Public Road Administration Rune B Abrahamsen Sweco Egil Rønnekleiv Plan architects
Existing situation
● Location: Alvdal municipality. Hedmark County, 300 km north of the capital Oslo.
● Existing bridges build in1953 and 1983
● The main bridge is in a bad condition
● High maintenance costs.
● A preliminary study in 2010 concluded that both should be replaced
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Network arch bridge and a glulam truss bridge
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To alternatives was considered in the end of the preliminary study. The study was performed by: NPRA, Sweco technical consultants and PLAN architects. The network arch was chosen as the preferred alternative.
Architectural comments
● Steien network arch bridge in one span over the river Glomma will provide an innovative and elegant design with strong identity and architectural quality.
● Double timber arches connected with diagonals in tension made of plates in stainless steel, along with a slender network, gives a very light and airy superstructure with a good side visibility and transparency. The bridge will appear as a new landmark in Alvdal.
● Walkways on the outside of the network planes provide a good contact with the river scenery.
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Some general facts ● Span: 88.0 meters
● The bridge carries two traffic lanes, 8 meters wide, and two 3 meters wide pedestrian walkways. Total 19 meters wide.
● Cross section of arches: w x d = 850 x 600 mm
● Height from centre slab to centre lower arch: 14 meters
● Distance between the centrelines of two arches: 1.25 meter
● Spacing of hangers and diagonals along the arches: 2.5 meters
● The slab is made of in situ casted light weight aggregate concrete with prestressing.
● Hangers: ø48 mm tension bars.
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FINAL DESIGN
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Characteristics of an optimal network arch bridge (Tveit 2011):
• Deck made out of concrete
• Ties imbedded in the deck in the form of prestressing cables.
• Arches made as part of a circle
• The upper node of the hangers are evenly spaced along the arch and
the hangers not being merged in the nodal points. • Most hangers crossing at least two other hangers
Definition of a network arch bridge
Structural performance compared to a typical tied arch
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Distribution of moments and compressive forces due to asymmetric loading. Steien arch bridge
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Experience from other network arch bridges
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DETAILS
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DETAILS
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DETAILS
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DETAILS
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Construction of the bridge
● When the interim route is established the road bridge and footbridge are demolished.
● Abutments are established prior to or simultaneously with the framework for bridge deck being established.
● Framework established on filling and / or temporary piles, optionally also using existing pillars.
● The slab is casted independent of the arches
● Each arch can be pre-assembled on factory and mounted on site in 4 segments.
● To compensate for the deflection the slab is casted with a camber. After stressing the slab will be jacked with an additional camber in order to ease the mounting of the hangers and reduce the need of hanger adjustments
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Utilization of the arches
● Total weight of the superstructure: 2264 tons
● Total traffic loading: 495 tons
● Ratio between self-weight of the superstructure + traffic loading and self-weight alone:
2760 tonns / 2264 tonns = 1.22
● Knowing that the long term modification factor for strength is 0.6, and the same factor for combined loading of self-weight and traffic is 0.9, giving a ratio of 1.5, it is possible to explain why self-weight is governing the design.
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Traffic loading
Position Double axel load (BL) Equal Distributed load
Axel load αQi ∙ Qik [kN] αqi ∙ qik [kN/m2] Loading area nr 1 1,0 ∙ 300=300 0,6 ∙ 9= 5,4
Loading area nr 2 1,0 ∙ 200=200 1,0 ∙ 2,5 = 2,5
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Loadmodel 1 according to NS-EN 1991-2:2003
Equally distributed load on the pedestrian carriageways are
q=5,0 kN/m2 without simultaneous traffic loading
q=2,5 kN/m2 with simultaneous traffic loading
1st buckling mode
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Buckling factor = 8 Selfweight alone
Thank you for your attention
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